Abstract: By the method of computational fluid dynamics，the three-dimensional unsteady flow field in labyrinth gas seals is predicted and the rotordynamic coefficients of the rotor are studied with approximate analytical transformation and scheme of hybrid finite analytical method. The reliability of the code is confirmed by comparing with the results of experiment and two-control-volume model. This code has the powers of studying the complex 3D unsteady flow field in complicated gas seal with arbitrary whirl of rotor. The results also show that the direct stiffness and the direct damping change small and the cross-coupled stiffness changes large if inlet tangential velocity changes large. Because the cross-coupled stiffness has the important effect on the stability of rotor, this phenomenon is utilizable.

Key words: Labyrinth gas seals, Rotor dynamic coefficients, Three-dimensional unsteady flow field